Such a steering unit is known, for example, from U.S. Pat. No. 4,676,334.
Such a steering unit can be used to steer a vehicle, i.e. to change the running direction of steered wheels of the vehicle. To this end a steering motor is connected to the working port arrangement. When a steering wheel or another command giving means is actuated, hydraulic fluid from the pressure port is guided to the working ports through the bridge arrangement. When, for example, the vehicle should be steered to the left, the first left orifice and the second right orifice are opened, so that hydraulic fluid enters the steering motor on one side and hydraulic fluid displaced from the steering motor flows back through the right working port and through the second right orifice to the tank port.
In some cases a secondary flow unit is connected to the working port arrangement. The secondary flow unit can supply hydraulic fluid to the working port arrangement which hydraulic fluid is not controlled by the steering unit, but by another unit which is, for example, GPS-controlled.
When the secondary flow unit supplies oil to the working port arrangement, situations can occur in which the driver feels uncomfortable.